Combatting Illness By Eating Well

How the right foods can keep your immune system in top shape.

How many times have you gotten yourself into terrific shape, only to come down with a cold the week before your big race? Or perhaps you make it to the finish line, but you can’t run a step for the next 10 days as you recover from strep throat or flu. What’s going on? For the most part, running seems to confer a protective effect against colds and other upper respiratory tract infections. In fact, most runners report suffering from fewer colds when compared to sedentary folks.

You’re not alone, though, if you feel particularly vulnerable to illness during periods of heavy training or immediately before or after an important race. Many elite athletes have been undone by colds and other viruses. Alberto Salazar reportedly caught 12 colds in 12 months while training for the 1984 Olympic Marathon. Competing with an obviously overstressed immune system, he finished 15th after entering the race as one of the favorites. In hopes of preventing a run-in with the sniffles (or worse), many runners down large doses of nutrients commonly believed to strengthen the immune system, such as vitamin C, zinc and glutamine. Avoiding sick people and large crowds is another strategy. You may, however, have overlooked one of the simplest, but most effective means of bolstering your immune system. A growing body of evidence suggests that paying attention to what you eat and when you eat it can have dramatic effects on your ability to thwart the common cold and other infections.

Running from Viruses

The study of how exercise effects the body’s immune system dates back to the turn of the century, but it wasn’t until the early 1990s that researchers really began to look at the immune systems of athletes. They found that despite the supposed protective effect of exercise, the immune systems of athletes are surprisingly similar to those of non-athletes. The only notable exception is that very fit people possess natural killer cells that are more active, which could give these individuals a greater ability to detect and destroy threats such as viruses and even cancer cells.

It’s after exercise—particularly prolonged, intense bouts—that many components of the immune system exhibit adverse changes. "There is an ‘open window’ or downturn of the immune system which lasts several hours to a few days," contends David Nieman, D.P.H., professor of health and exercise science at Appalachian State University in Boone, NC, and one of the country’s leading exercise immunologists. Depending on other factors, such as poor eating habits, inadequate sleep and mental stress, a particularly intense or long running effort may be the final blow to an overtaxed immune system. Viruses and bacteria can gain a foothold at this time, disrupting your training and racing plans.

The Power of Carbohydrates

Nieman, himself an avid runner, finds little conclusive evidence that vitamin C, zinc, glutamine or other popular nutritional supplements can influence an immune system suppressed by prolonged, intensive exercise. So he was just as skeptical when he began researching the possibility of boosting immune function by using a carbohydrate beverage during exercise. "I really didn’t think it would work," he says. "I’ve seen these immune system changes occur [as a result of exercise] in study after study and I didn’t think that anything could turn it around."

Following several double-blind placebo-controlled trials (neither Nieman nor the subjects, who included marathon runners, knew who was drinking the carbohydrate-containing beverage) he’s impressed with the results. "In every case, all the athletes on the carbohydrate beverage showed little change in their stress hormones," says Nieman. This suggests these athletes experienced less stress to the immune system than those who received the placebo.

Consuming carbohydrate during exercise appears to boost the immune system by preventing precipitous dips in blood sugar. A low blood sugar level causes the body to release large quantities of stress hormones, particularly cortisol. Typically elevated after prolonged or intense exercise, cortisol profoundly suppresses immune function. In a nutshell: Take sugar in and keep your glucose up during exercise and your cortisol levels will be significantly lower. And that may be the edge you need to keep a cold, sore throat or the flu at bay.

Runners who train or compete frequently for 90 continuous minutes or more—sound like anyone you know?—should benefit the most from consuming carbs on the run. According to Nieman, at 90 minutes "all of a sudden the body’s glycogen stores are getting severely depleted, water is going down if you’re not drinking and your body temperature is going up and your brain starts to interpret all this as stressful. Carbohydrate supplementation really becomes an issue to help counter the negative changes routinely seen in immune function."

Drinking water should be sufficient during training efforts lasting 60 minutes or less. If you’re going longer or tackling a particularly strenuous workout, use a sports beverage or other easily tolerated source of carbohydrate, such as diluted juice or water and an energy gel. Not only will you improve performance by delaying dehydration and maintaining a high blood-sugar level during exercise, you may also lower your risk of falling prey to an infection.

Day-to-Day Counter-Measures

Beyond quaffing sports drinks during your long runs and races, you can also bolster your immune system by improving your day-to-day eating habits. Eating a variety of foods, including an adequate amount of carbohydrate- and protein-rich items, will help keep the body’s vitamin and mineral pools at optimal levels. Maintaining a healthy weight also makes sense, as rapid weight loss has been linked to negative immune changes. Eating a diet too low in fat may compromise your immune system, although it’s too early to draw conclusions from the existing research.

How you consume your calories throughout the day can also make a difference. Dan Benardot, Ph.D., R.D., co-director of the Laboratory for Elite Athlete Performance at Georgia State University, contends that runners who consume most of their calories after their daily training place a great stress on their immune system. "Consuming 80% of the food you need during the evening means you’re not in energy balance during the day," reasons Benardot. "We know this is counter-productive to athletic performance and it’s logical that it would be more stressful to the immune system, since your blood glucose will be hitting peaks and valleys throughout the day."

To normalize your blood-sugar level during the day, closely balance the calories you consume with the calories you expend. Benardot advises runners to think about their energy needs on an hour-to-hour basis, not just from day to day. "Most runners know their training and work schedules when they leave the house in the morning. Give the same thought to your eating schedule," he suggests. Avoid going long periods without eating, which can lead to wide swings in blood sugar. Even though heavy training can reduce your appetite, commit to eating every three to four hours while awake. Plan ahead to have healthy foods on hand when you’ll need them and always go into workouts well fueled. Besides giving you more energy to train, these strategies will keep your immune system in better shape to fight off the latest cold making the rounds.